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# Centrifugal fan motor having same KW at 50 and 60 Hz3

## Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)

Don't the fan affinity laws for centrifugal fans say that power is proportional to cube of the speed?

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

Just because the nameplate rating for the max current or power allowed before the smoke comes out is the same at either frequency, doesn't mean the actual (hopefully smaller) running current or power will be the same!

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

Looking pretty ridiculous to me.

Doing the straight 3ph calcs the two conditions don't even make sense individually.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

Hmm yes I was thinking the same, but calculating with effectiveness you get pretty close.
I guess what looks lik pf on the right side of the plate 0,79 is cos fi but I am not sure.

1,73 x 400 x 4,6 x 0,82 x 0,843 = 2200 W
1,73 x 690 x 2,65 x 0,82 x 0,843 = 2186 W
1,73 x 460 x 4,05 x 0,79 x 0,875 = 2227 W

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
All power calculations work out to nearly 2.2 KW for both speeds and for all 3 voltages. Unfortunately, don't have a source or a system to run the fan at 60 Hz to verify the power.

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

Edison - You are correct.

The fact the max power of the motor at 50Htz, doesn't mean that is what it is doing.

If they've sized the motor able to provide the power to the fan at 60 Htz / 1755 rpm, then it's all good.

If not then it's all bad.

So how much current does it actually suck in at 50Htz?
Plus if you specified the motor / fan to run off 50Htz, what's the issue?
Change the frequency of supply to your motor, things are going to change.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
Littleinch - The fan current was 4.5 A (rated is 4.6 A) at 400 V, 50 Hz.

I didn't spec the fan motor. This came to my shop as part of servicing a 450 KW VFD motor. The nameplate KW didn't make sense to me for the higher speed given the fan laws.

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

2.2kW is motor nominal power (output), not power requested by fan.
All nameplate data refer to motor not fan.
Fan power requested at 60Hz are sure below 2.2kW... at 50Hz even much lower.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

edison,

The motor and the fan are two separate things - they weren't made an a single thing, but joined together at a later stage.

Clearly whoever bought the fan specified 50Htz 400V power supply so the motor was chosen to match the fan requirement which is clearly JUST within the motor capacity. Now stick 460V 60 htz into the same fan/motor combination and sure, you will start overheating / tripping the motor rather rapidly as it will consume about 3.8 kW...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
iop - The fan requires nearly 2.2 KW at 50 Hz as shown in above testing.

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
Little - That's my point. The nameplate is misleading. Siemens supplied the whole caboose as a package, motor, fan and all.

Even assuming the motor and the fan were assembled later, the motor should be rated 20% more power at 60 Hz, not the same 2.2 KW of 50 Hz.

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

Yes they did, but clearly in a package where the power supply was 50 htz. If the power supply was 60 Htz they would need to reduce the size of the fan supplied.

It's a bit odd the way they've done it alright, but maybe all they wanted is a fan with a power of 2.2 kW so built a motor to do just that, regardless of whether the power supply was 50 or 60 htz so they could use the same wiring, fuses, breakers etc etc. Now they would need to remember to install the 60htz fan, but the Germans are quite good at their QA....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

The motor was selected appropriate for the given fan duty with 50Hz power supply.
The motor is not expected to run the same fan with 60Hz power supply.
The details given on the nameplate for 60Hz power supply are redundant / not relevant in this case, I suppose.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

@edison123
Ok, I saw now that current is 4.5A at 400V/50Hz.
May use a VFD (auto/transformer step up to 460V or direct to DC bus with 620Vdc) to test at 60Hz.
I think tests must be performed in original encolsure fan configuration. May be pressure difference that lead to other working points on fan curve.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

I agree with those who said the nameplate applies soley to the motor, nothing to do with the fan. The nameplate includes IEC and NEMA terminology relating to motors. It doesn't say a single thing about anything to do with the fan (flow rate or dp).

I presume there is a separate nameplate somewhere that talks about the fan. I'm not sure what we can say about the fan operating point and bhp. In some cases those parameters depend not just on speed and the fan characteristics but also the system to which you connect it (to determine intersection of fan curve and system curve). There may be some designs that strive to prevent motor overload regardless of the connected system, but I don't think that is universal.

The motor output power rating presented in the two different systems (IEC and NEMA) is numerically the same at 400v/50hz and 460v/60hz (both 2.2kw) but it has probably has more margin when operating 2.2kw at 60hz (since the current associated with that power is lower at 460v/60hz). Depending on how you look at things, the 1.15SF also implies you have some margin in the 460v/60hz rating. All in all, we can confidently say you could safely operate the motor at a somewhat higher kw output when supplied by 460v/60hz (possibly up to 60/50~20% higher). The factor by which you can safely increase kw is probably not as much as the (6/5)^3~1.7 theoretical increase in bhp for a fan but again we have some unknowns about the fan operating conditions in relation to motor rating, not to mention the connected system. Assuming there is no assumed change in the connected system, it may well be that the motor ends up being far oversized for the fan load presented at 50hz and has only razor thin margin to the fan load presented at 60hz.

=====================================
(2B)+(2B)' ?

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

edison123 The MOTOR nameplate is for the MOTOR. It tells you what shaft output power (at what applied voltage) it can safely deliver while remaining within the thermal and mechanical limitations of the MOTOR design. The MOTOR was designed as a MOTOR - it could be used on pretty much anything requiring that power/speed combination.

Someone somewhere along the line chose a fan assembly where the wheel and scroll configuration put the power requirement at defined speed such that the 2.2 kW rating at some nominal speed (slip speed at the rated frequency) is sufficient to produce the desired airflow (i.e., volume and pressure). This is also pretty typical.

The big question is: what is the design INPUT voltage for the VFD? This will (hopefully) tell you whether the machine was intended for the IEC world (50 Hz) or for the North American market (60 Hz). If the motor is already drawing near nameplate current when operated on a 50 Hz supply, then the fan wheel is NOT sized for 60 Hz operation and will overheat if so applied, as the fan loading will require more power than the motor can provide (safely).

Converting energy to motion for more than half a century

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
Leaving aside the fan and considering only the motor, why would it have the same output at higher frequency?

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

Motors can only respond to the load that they are being put under. They don't "output" a load, they respond to the load that is trying to slow the motor down.

At "no load" there is still some current, but the motor is spinning at either 1435 or 1755 rpm or maybe a bit faster at no load. If there was nothing attached to the motor then its power consumption would be much lower.

So in this case, put a bigger fan on it and the load goes up.
Spin the same fan faster and the load goes up.

The motor vendors have clearly decided that the motor is only suitable for providing a load of 2.2kW.

It is up to the designer to ensure that the load does not exceed 2.2 kW or the motor will either get rather hot or trip on excess amps. Or both.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
Little

As I said, consider the motor only. A 50 Hz to 60 Hz operation automatically upgrades the motor capacity by 20%. Nameplate should reflect it.

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

"automatically upgrades the motor capacity by 20%" - No it doesn't. It just makes it go 20% faster.

If the load is the same at both speeds then the capacity is the same at 50 and 60 htz. Now what tends to happen unless you modify it is that as the connected load goes faster, then its load increases. But if you modify the load so that at the higher speed the load is the same as it was at 50hts, then the "capacity" is the same.

The name plate is correct because it was put there by the manufacturer. There may be things in the motor that are not suitable for a higher current or higher power.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
Little - If V/Hz is maintained, the motor power does go up. Simple math.

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

What happens to losses when the voltage, frequency, and mechanical load all increase? Perhaps the manufacturer doesn't consider the motor cooling to be sufficient to handle higher losses at 1755RPM.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

V/Hz it's not maintained.
Frequency ratio: 60/50 = 1.2
Voltage ratio: 460/400 = 1.15... so at 60Hz flux is lower with 4.3%, that mean about 8.9% lower torque than at 50Hz.
Even rated speed ratio is about 1.22 that don't mean 1.22x more power at 60Hz because torque at 60Hz is lower.
One standard motor power value is 2.2kW and even that motor from design calculation and in real tests has maybe 2.4-2.5kW it was rated at 2.2kW.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

Muthu,
I think that is not a centrifugal fan, it is axial, so the affinity laws for centrifugal loads don’t apply. They likely know that at 120% speed on 60Hz, that fan doesn’t move any more air.

But to your point on what the motor nameplate says, I agree, but there is a slight catch here. The 2.2kW is a MECHANICAL output rating, meaning a specific amount of torque at a specific speed. If the torque stays the same and the speed increases by 20%, the kW increases by 20%. The only way the kW rating could stay the same is if the torque DECREASES when the speed increases. That would happen if you gave it 400V at 60Hz, but by giving it 460V, the V/Hz ratio is almost the same as it is at 400/50.

And that “almost” might be the issue here. By rating it at 460V, not 480V, the calculated kW at the higher speed but slightly reduced torque comes out to only 2.3kW, which is within 5% of the 50Hz rating, but not a standard rating, so maybe they just called it close enough.

That’s kind of not like Siemens though to be honest…

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

#### Quote:

Little - If V/Hz is maintained, the motor power does go up. Simple math.
A 50 Hz to 60 Hz operation automatically upgrades the motor capacity by 20%.

I agree with you on that point at least to a good approximation (and setting aside that the v/hz is not quite maintained as iop95 mentioned). Itsmoked gave us a FAQ on the subject FAQ237-1224: Motors: Changing between a 50 and 60Hz supply.

The two nameplate ratings are based on two different standards (IEC and NEMA). The NEMA rating has a lower current, so I'd say you clearly have more thermal margin built into the NEMA 2.2 kw 460v/60hz rating than in the IEC 2.2 kw 400v/50hz rating. If you're so inclined you could ignore the NEMA standard rating and look instead at the NEMA SF rating 1.15 and I'll be it ends up with ballpark similar thermal margin as the IEC rating in this particular case.

I don't know the details of how those two standards (NEMA vs IEC) compare on thermal margin in general.

=====================================
(2B)+(2B)' ?

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

(OP)
OEM's use one single frame for 2,4,6 poles to get decreasing outputs. The rating definitely is proportional to speed. That's why americans went for 60 Hz, more bang for the buck. Also, higher the speed, better is the efficiency.

Jeff, it's a centrifugal fan - axial suction and radial delivery.

Muthu
www.edison.co.in

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

I'd say it's the service factor making the difference. A 1.0 service factor would mean the 60Hz rating is 2.5kW, about what would be expected compared to the 50Hz rating.

### RE: Centrifugal fan motor having same KW at 50 and 60 Hz

2
A tricky nameplate.
It is not a general purpose motor but a special one for particular applications (part of bigger machine). Thus, you cannot completely rely on the data from the nameplate.
You can design a motor eg. for 3 kW; 460 V; 60 Hz and mark it on the nameplate as 2.2 kW .
Such a motor will be capable of delivering 2.2kW at 400V, 50Hz for sure.

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